solidify modifier adding non uniform thickness to the mesh
You must have scaled your object in Object mode rather than Edit mode. If you do it in Object mode, Blender still considers the original size of the object when you'll assign it a Solidify modifier.

So you need to select your object and ctrl A > Apply Scale, so that now the scale you've made is applied to the mesh itself and not only to the object.

Also, enable the Even Thickness of the modifier, it could prevent some other distorsions.

And at last, your object mesh must be a little bit messy because you have strange artifacts, try to make a clean topology.